Ok folks,

I found it. Here is how I managed to fix the error:

1. Open a terminal window (root is not necessary).
2. cd /home/user/.FBReader
3. rm state.xml

When you reopen FBreader, it should open normally. The brute force method would be to remove the .FBreader directory and then reopen FBreader, but then it would delete all of your settings, including, I think, your bookmarks in whatever books you have open.

Hope that helps someone...

--vr